In such methods, a support is frequently used as a donor structure: a portion of the donor structure (generally a superficial layer) is used as an element of the target structure, for example by means of a layer transfer.
This solution is encountered in particular for making a germanium on insulator (GeOI) type structure, for example as described in the papers “Germanium-On-Insulator (GeOI) structure realized by the Smart Cut™ Technology”, by F. Letertre et al. in Mat. Res. Soc. Symp. Proc. Vol. 809, 2004 Materials Research Society, and “200 mm Germanium-On-Insulator (GeoI) Structures realized from epitaxial wafers using the Smart Cutt™ technology”, by C. Deguet et al., ECS 2005, Quebec, vol. 2005-05, page 78.
Those papers propose two alternative solutions for transferring the thin germanium layer that forms the superficial layer of the GeOI structure: the donor wafer used is either a bulk germanium wafer or a silicon wafer on which a germanium layer has been epitaxially deposited, at least a portion whereof will be transferred.
The solution using bulk germanium is advantageous from the electrical point of view in particular because of the very high crystalline quality of the transferred material (the proportion of dislocations in the bulk germanium is close to zero), but the manipulation of bulk germanium is relatively complex, in particular because of the high density of this material and its mechanical weakness.
This is why at present it is envisaged instead to use in practice as the donor wafer the germanium-based structure deposited epitaxially on silicon already mentioned.
However, using this solution as proposed in the papers already cited sometimes produces layers of germanium having a proportion of dislocations of the order of a few 106 cm−2, essentially generated during the phase of epitaxial deposition of the germanium on the silicon because of the lattice parameter difference between the crystalline arrays of these two materials (Δ=4.2%).
Generally speaking, it can be beneficial to use as the donor wafer a structure consisting of a first material deposited epitaxially on a second material (for example to benefit from the electrical properties, or more generally the physical properties, of the one and the mechanical properties of the other). If these two materials have different lattice parameters, this type of solution leads, however, unless particular precautions are observed, to a relatively high proportion of dislocations in the layer of the first material, which can degrade the electrical and/or physical properties of that layer.